FIELD OF THE INVENTION
Microporous silica aerogel and xerogel structures are described which are suitable as thermal insulation. These xerogels and aerogels are produced by the process described herein which carefully controls the ratios of ingredients, catalyst, and solvent.
Thermal insulation is an important and valuable product. Although many insulative compositions are already in use, there is a continuing desire for energy conservation pushing a drive to achieve insulation having lower thermal conductivity. Microporous silica aerogel structures have excellent characteristics for insulation.
One reference which describes such silica structures is "Rubbery Ormosils and Their Applications" by John D. Mackenzie Journal of Non-Crystalline Solids, 147&148 (1992) 271-279. In that reference, organically modified silicates (ormosils) are produced using silanol terminated polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) in a mixture of ethanol, HCl and water using a molar ratio of 1TEOS/0.08PDMS/3H2O/0.3HCl. The materials produced by the methods of this reference, however, do not give highly microporous structures. To the contrary, the pores are large, and as a result, the thermal conductivity is disadvantageously high.
It would be advantageous to obtain silica aerogels and xerogels having a microporous structure and a better thermal conductivity. Accordingly, it is an object of the present invention to achieve microporous aerogel and xerogel structures which are good thermal insulation. It is a further object of the present invention to achieve processes which result in more highly microporous aerogel and xerogel structures.